Anthropic has opened public access to its AI model Claude Fable 5 and launched Claude Mythos 5 for a select group of partners in Project Glasswing.
Both models are built on the same underlying architecture, with the key difference being that Mythos 5 operates without some of the standard safety restrictions.
Claude Mythos 5 has been deployed as part of Project Glasswing, a collaboration initiative with the U.S. government. This model is an upgrade from the Claude Mythos Preview, which was made available in April to a limited group of cybersecurity experts and providers of critical software infrastructure.
In the future, Anthropic plans to grant access to Mythos 5 to individual researchers in biology and participants in the trusted access program.
The Fable 5 model is available to all users via the Claude API and consumption-based Enterprise plans. For Pro, Max, Team, and seat-based Enterprise subscriptions, there is no additional charge for its use until June 22, 2026. After June 23, credits will be required to use it unless the company extends the grace period.
Fable 5 includes a mechanism for redirecting queries related to cybersecurity, biology, chemistry, and model distillation to the more powerful Claude Opus 4.8. According to Anthropic, this fallback occurs in less than 5% of sessions on average.
The cost for using both models is $10 per 1 million input tokens and $50 per 1 million output tokens.
As a reminder, in May, Anthropic released Claude Opus 4.8 and separately introduced a dynamic workflows feature for Claude Code.